This kind of compaint (finding a piece of carrot) happens in various products in various suppliers. It's a mystery...
In that case I agree with The Food Scientist - this may be due to ineffective cleaning / line clearance controls at your suppliers.
It does sound odd that the same problem is affecting different products from different sources though.
I think I'd do two things in your position:
1) Contact your suppliers, as if the problem is happening at their sites then they need to address it. Ask them to investigate the complaints, identify the root cause, and implement corrective action accordingly - it sounds like this may end up requiring a combination of an improvement to cleaning procedures and a more thorough sign-off after cleaning has been completed, but they'll need to determine that. I'd also ask them what the current cleaning regime is prior to packing each of the affected products.
2) I'd review the customer complaint details just to see if there is any apparent pattern in the names/addresses of those making the complaints. I'm a bit cynical (a life in the food industry can do that to you ) but a spate of unusual complaints does make me slightly curious as to whether the issue is real, or if it could instead be being used by complainants as a way to try to get free products / refunds. This does sound somewhat unlikely here, given that your post suggests the numbers of complaints are large, but nonetheless it's worth checking.